System and method for performing bulge testing of films, coatings and/or layers

ABSTRACT

A system and corresponding method for bulge testing films (e.g. thin films, coatings, layers, etc.) is provided, as well as membrane structures for use in bulge testing and improved methods of manufacturing same so that resulting membrane structures have substantially identical known geometric and responsive characteristics. Arrayed membrane structures, and corresponding methods, are provided in certain embodiments which enable bulge testing of a film(s) over a relatively large surface area via a plurality of different freestanding membrane portions. Improved measurements of film bulging or deflection are obtained by measuring deflection of a center point of a film, relative to non-deflected peripheral points on the film being tested. Furthermore, membrane structures are adhered to mounting structure in an improved manner, and opaque coatings may be applied over top of film(s) to be bulge tested so that a corresponding optical transducer can more easily detect film deflection/bulging. In certain embodiments, a laser triangulation transducer is utilized to measure film deflection/bulging.

This application is a divisional application of a previous patentapplication, U.S. Ser. No. 08/955,928, filed Oct. 22, 1997, which hasnow issued as U.S. Pat. No. 6,050,138 granted on Apr. 18, 2000.

This application relates to an inexpensive, accurate, and efficientsystem and method for performing bulge testing of films, coatings,and/or layers. More particularly, this invention relates to improvedsystems and methods for performing bulge testing of such films,coatings, and/or layers, including improved methods of manufacture,improved membranes for use in such testing, improved methods formanufacturing membranes, improved testing components, improved testingprocedures, and improved materials for use with same. Systems andmethods herein enable the determination of elastic properties, inelasticproperties, time-dependent properties, residual stresses, and the likeby measuring the bulging of a membrane and/or film when one side thereofexperiences an increase or decrease in pressure. In certain alternativeembodiments, bulging caused by inherent pre-stress (without applicationof pressure or evacuation) in the film is measured to determine theaforesaid properties.

CLAIM TO COPYRIGHT IN REFERENCE TO APPENDIX

An appendix portion of the disclosure of this patent applicationcontains material which is subject to copyright protection (see FIGS.15-70). 37 C.F.R. §1.96(a)(1). The copyright owner has no objection tothe reproduction by anyone of the patent document as it appears in thePatent and Trademark Office files or records, but otherwise reserves allcopyrights whatsoever. Instructions for software for carrying out someof the methods and systems, has been filed with the United States Patentand Trademark Office herewith as FIGS. 15-70.

BACKGROUND OF THE INVENTION

It is known that properties of a film, coating, or layer of a givenmaterial differ from those of the same material in bulk form. Forexample, thin films have different yield stresses, creep behavior, andelastic properties than do bulk forms of the same material. The only wayto determine the qualities or properties of thin films is to measure thefilms themselves.

As technology advances, many elements including storage media (e.g.disks), integrated circuits, cutting tools, sensor arrays, wearsurfaces, LCD matrix arrays, and the like include films, coatings,and/or layers deposited on a substrate. The term “film” as used hereinis to encompass films, coatings, and layers of varying thicknesses.Typically, each film (e.g. thin film) has different residual stresscharacteristics and different thermal and/or mechanical properties,which may affect the performance, reliability, or durability of devicesincluding such films. The ability to determine mechanical properties andresidual stress characteristics of thin films is thus desired. Bulgetesting is one way in which to do this.

In prior art bulge testing systems, as shown in FIG. 1, circular orrectangular film 1 having a thickness “t” is clamped over cavity ororifice 3 in mounting structure 5, and pressure is applied to the bottomside of film 1 from within the orifice. The out-of-plane deflection orbulging of film 1 is measured as a function of the applied pressureenabling determination of a pressure-deflection curve and the residualstress in the film. Prior art FIG. 2 shows the vertical equilibrium offilm 1 when pressure is applied via cavity 3.

The stress state of film 1 is two dimensional so that properties in theplane of film 1 are measured through the use of known equations whichinclude as parameter(s) the geometry of the film, the properties of thematerial composing the film, the differential pressure applied acrossthe film, the center deflection of the film, and in-plane residualstress. For example, see “Mechanical Properties of Thin Films” by Nix,found in the 1988 Institute of Metals Lecture, Volume 20A, November1989; “Measuring the Mechanical Properties of Thin Metal Films by Meansof Bulge Testing of Micromachined Windows” by Paviot, et. al., Mat. Res.Soc. Symp. Proc. Vol. 356, 1995 Materials Research Society; “MechanicalBehavior of Thin Films” by Vinci and Vlassak, Annu. Rev. Mater. Sci.1996-26:431-62; “The In-Situ Measurement of Mechanical Properties ofMulti-Layer Coating” by Lin, 1990 MIT Dept. of Mat. Sci. & Eng.,Archives; “Load Deflection Analysis for Determining MechanicalProperties of Thin Films With Tensile and Compressive Residual Stresses”by Bulsara, 1995 MIT Dept. Mat'l. Sci. & Eng.; and “New ExperimentalTechniques and Analysis Methods for the Study of the Mech. Prop. ofMaterials in Small Volumes”, Chapt. 3, by Vlassak (1994), thedisclosures of which are all hereby incorporated herein by reference.

Bulge testing of circular or square freestanding windows of differentgeometries of film 1 mounted to structure 5 allows one to determine thebiaxial modulus of the film as well as the residual stress in the film.Knowledge of these characteristics is important in determiningdurability and other mechanical and structural characteristics of thefilm.

With regard to square films or membranes, for example, the elasticdeflection as a result of a uniform pressure “p” applied in the cavityis known to be approximately described by the following equation (seePaviot, et. al. referenced above):$p = {{{c_{1}(v)}\frac{Et}{( {1 - v} )a^{4}}w_{0}^{3}} + {c_{2}\frac{\sigma_{res}t}{a^{2}}w_{o}}}$

where c₁(v) is about 1/(0.792+0.085 v)³ and c₂ equals about 3.393. Inthis expression, w₀ is the deflection of the center of the film ormembrane, “t” is the film or membrane thickness, and “a” is the width ofthe membrane. Utilizing the above-identified equation enables one todetermine the biaxial modulus Y=E/(1−v) and the residual stress in thefilm.

As disclosed in Vinci and Vlassak (cited above), the pressure-deflectionrelationship for a thin circular film or membrane with a residual stressin a bulge test is approximated by the equation:$P = {{( {1 - {0.241v}} )( \frac{8}{3} )( \frac{E}{1 - v} )( \frac{t}{a^{4}} )w_{0}^{3}} + {4( \frac{\sigma_{0}t}{a^{2}} )w_{0}}}$

in the elastic regime, where wo is the deflection of the center of thefilm or membrane, “P” is the applied pressure, “t” is the film ormembrane thickness, and “a” is the film or membrane radius. Using thisequation enables one to determine the biaxial modulus E/(1−v) and theresidual stress in the film.

It is noted that other equations, which are disclosed and explained inthe above-identified publications, may be used to determine residualstress and/or elastic modulus of films subjected to bulge testing.

It is also known to test composite membranes including two or morelayers. For example, see pages 90+ in Chapter 3 of Vlassak, “NewExperimental Techniques and Analysis Methods for the Study of theMechanical Properties of Materials in Small Volumes” (1994), where bulgetesting of a composite membrane including two or more layers isdiscussed. As discussed by Vlassak, silicon oxide or silicon nitridefilms can be used as substrates or membranes onto which metal films aredeposited. This technique can be applied to a variety of films withoutmajor changes to the sample preparation method.

Still referring to Chapter 3 of Vlassak, pages 90+, it is known that theresidual stress in, and elastic properties of, the silicon nitride orsilicon oxide membrane by itself can be determined by bulge testing themembrane without a film overlayer. Thereafter, when a metal overlayerfilm is deposited onto the silicon oxide or silicon nitride membrane,its biaxial modulus can be calculated from the biaxial modulus of thecomposite film. If Poisson's ratio of the metal film is known, Young'smodulus of the metal film can be calculated from the biaxial orplane-strain modulus. The residual stress in the metal film iscalculated via the average residual stress in the composite, as theweighted average of the stresses in the membrane and the metal filmoverlayer.

As discussed in section 3.4 of Vlassak, Chapter 3, it is known tofabricate freestanding silicon nitride films on silicon substrates byway of micromachining. Such silicon nitride membranes are then used assubstrates or membranes for other films (e.g. metal films) and theresulting composite film is bulge tested. Referring to prior art FIGS.3(a)-3(f), known steps are shown in a sample preparation process. Asillustrated in FIGS. 3(a) and 3(b), silicon nitride films 7 withresidual tensile stress are deposited by LPCVD on both sides of wafer 9.Using mask 11 illustrated in FIG. 3(c), a window is etched in siliconnitride film 7 on the backside of the wafer by way of lithography andreactive ion/plasma etching. The etched window is illustrated in FIG.3(d). Thereafter, as shown in FIG. 3(e), silicon 9 exposed by thepreviously etched window is etched using, for example, an etchantincluding potassium hydroxide. FIG. 3(e) illustrates the final siliconmembrane wafer structure with a freestanding flexible silicon nitridemembrane over the cavity on its top surface. The freestanding flexiblemembrane portion of layer 7 in FIGS. 3(e)-3(f) is defined within thesilicon shoulder area, where film 7 is susceptible to bulging. Finally,as illustrated in FIG. 3(f), a thin metal film 13 to be bulge tested isevaporated onto the top surface of the membrane structure.

After the FIG. 3(f) structure is made, as disclosed by Vlassak, it isbulge tested using the prior art FIG. 4 apparatus, which includesmounting structure 15 upon which composite sample member 17 to be bulgetested is mounted, pump 19, pressure gauge 21, computer and dataacquisition terminal 23, and an inspection system for detectingdeflection of film 17. The inspection system including laser 25,beamsplitter 27, collimator 29, lens 31, reflective mirror 33, densityfilter 35, reference mirror 37, and screen 39 with an interferencepattern. As described by Vlassak, sample 17 to be tested is glued ontomounting structure 15 and pressure is applied to the lower side ofsample 17 by pumping water into cavity 41 via pump 19. The inspectionsystem then measures the deflection of sample 17 caused by the waterpressure in the cavity. The result is a pressure versus deflection plotfor the sample. From this plot, the elastic modulus and residual stressof overlying film 13 can be determined.

U.S. Pat. No. 4,735,092 to Kenny, discloses a rupture testing apparatusfor classifying or grading metal foils. Gas under pressure is admittedto a platen and the unsupported part of the sample bulges outwardlyuntil the sample ruptures. A plot is made of samples for temperature,burst pressure, and bulge height at burst, with the results being usedto grade or classify the foil. Unfortunately, the '092 patent suffersfrom a number of problems, including the inability to efficiently andproperly determine stress and/or modulus characteristics of the filmbeing bulge tested. For example, the dial micrometer transducer includesa probe or arm which extends downward to contact the film being bulgetested. Contacting type transducers are generally undesirable,especially in view of the fragile nature of many samples that must betested. Further deficiencies in the '092 system are discussed below.

While the above-referenced prior art bulge testing techniques anddisclosures achieve satisfactory results in non-commercial environmentswhere cost and efficiency are not critical considerations, theyunfortunately have their limitations. A few of these limitations arediscussed below.

The characteristics and properties of films, coating, and layers used inelectronic arrays, wear surfaces, circuits, cutting tools, and the likeare becoming more and more important. Different systems and techniquesare utilized to deposit and/or pattern thin films on substrates. Forexample, a uniform thin film indium tin oxide (ITO) layer a few hundredÅ thick may be deposited across an entire substrate, and thereaftersometimes patterned via conventional methods into a plurality ofelectrode segments. Due to the techniques and systems used to depositand/or pattern such thin films, it is not surprising that areas of thethin film(s) on the substrate, or certain patterned electrodes in thearray, may have different residual stress and modulus characteristicsthan others. For example, film near an edge of the substrate may havedifferent stress characteristics than near the center of the substrate,due to the techniques and systems utilized in the deposition,fabrication, and/or patterning. For example, a continuous film may havedifferent residual stress and/or elastic modulus characteristics indifferent areas on the substrate. Differences such as these in largearea substrate or array-type applications cannot be detected by theprior art bulge testing systems discussed above.

Bulge testing has been minimally successful at best, for reasons such ashigh substrate/membrane costs, the inability to commercially manufacturescores of reproducible substrates/membranes within limited predetermineddimensional and compositional tolerances (i.e. very difficult andexpensive to make substrates of constant dimensions which all have thesame characteristics), inaccurate substrates/membranes, inability totest large area films, and the like.

There also exists a need in the art for reproducible circular, ratherthan square, membranes to allow analytical equations to be used tocalculate thin film mechanical properties from pressure-deflection datarather than having to use numerical methods. Also, a need exists formembrane material having reproducible mechanical properties in contrastto currently produced silicon nitride or silicon oxide whose mechanicalproperties vary as a function of deposition/growth parameters, andequipment used to manufacture same.

It is apparent from the above that there exists a need in the art for abulge testing system that can be utilized to test large area thin films(or portions thereof) on substrates, and thin film segments as they aredeposited in array form on a substrate. There is also a need in the artfor a way in which to fabricate supporting substrates/membranes so thaton a continuous basis all such supporting membranes are fairlyidentical, with their geometries, mechanical responses, and/or materialproperties being substantially the same. Therefore, in a commercialbulge testing environment, it would be desirable if there were no needto separately bulge test each membrane structure and determine itscharacteristics prior to applying thereto a thin film to be tested. Theability to mass produce many such uniform supporting membranes wouldresult in increased efficiency and significant cost savings incommercial testing environments. There also exists a need in the art foran improved membrane structure for supporting thin films to be bulgetested. Other needs include the need for precision mounting ofmembranes, automated measurement, improved deflection detectiontechniques, and improved software for manipulating the table or platformupon which the membrane structure is mounted.

It is a purpose of this invention to fulfill the above-described needsin the art, as well as other needs which will become apparent to theskilled artisan from the following detailed description of thisinvention.

SUMMARY OF THE INVENTION

Generally speaking, this invention fulfills the above-described needs inthe art by providing a method of manufacturing a plurality of membranestructures for use in bulge testing so that a majority of themanufactured membrane structures include freestanding portions havingsubstantially the same thickness, substantially the same in-planegeometry (e.g. diameter), and substantially the same response, themethod comprising the steps:

selecting at least one material to be utilized in the manufacture of themembrane structures;

forming portions of the at least one material into a plurality ofmembrane structures, each of the membrane structures including at leastone cavity and at least one freestanding thin film portion located overthe cavity and defining a surface of the cavity; and

using manufacturing techniques to manufacture each of the membranestructures so that at least about 85% (preferably at least about 95%) ofthe resulting membrane structures have identical freestanding thin filmportion geometries including (1) in-plane diameters, and/or (2)thicknesses, within about ±5% (preferably within about ±3%, and mostpreferably within about ±1%), thereby enabling commercial bulge testingto be more efficiently undertaken. The freestanding membrane portionsare preferably circular in shape (as viewed from above), but also may beother shapes such as rectangular, oval, etc.

This invention further fulfills the above-described needs in the art byproviding a structure for use in bulge testing of films, the structurecomprising:

a membrane structure including a plurality of cavities defined therein;and

a plurality of freestanding portions capable of bulging, each of thefreestanding portions corresponding to at least one of the cavities, sothat each of the freestanding portions defines part of a correspondingone of the cavities, and wherein each of the freestanding portions isadapted to receive thereon a film (e.g. thin metal film, thin ceramicfilm, thin paint coating, thin polymer film/resist, etc.) to be bulgetested.

According to certain preferred embodiments, the film to be bulge testedis preferably a thin film and may include one of a thin metal film, athin ceramic film, a polymer thin film, a coating, and a layer, andwherein the film to be bulge tested is from about 100 Å to 500,000 Åthick (preferably from about 100 Å to 50,000 Å thick, and mostpreferably from about 500 Å to 5,000 Å thick).

This invention further fulfills the above-described needs in the art byproviding an apparatus for bulge testing films, the apparatuscomprising:

a mounting structure including an upper surface and a cavity definedtherein;

means for positioning a film to be bulge tested on the upper surfaceover top of the cavity;

an optical transducer for measuring deflection or bulging of the filmproximate the cavity in a non-contacting manner, wherein the transduceris one of a white light interferometer and a laser triangulationtransducer; and

means for determining stress and modulus properties of the film basedupon measurements taken by the transducer.

In certain preferred embodiments, an opaque film is provided on top ofthe film to be bulge tested or under the freestanding membrane portion,in order to enable the transducer to more accurately and efficientlydetect deflection or bulging of the film to be bulge tested and theunderlying freestanding membrane portion.

This invention further fulfills the above-described needs in the art byproviding a method of bulge testing a thin film, the method comprisingthe steps of:

providing a bulge testing apparatus including a major surface and acavity defined therein;

providing a thin film on the major surface over top of the cavity;

locating a center point on the thin film, the center point overlyingapproximately the center of the cavity;

locating first and second points spaced from the center point, so that aline connecting the first and second points, and the center point,substantially bisects or otherwise crosses a portion of the thin filmoverlying the cavity; and

optically measuring bulging or deflection of the thin film by measuringdeflection of the center point relative to the first and second pointswhich are positioned at undeflected locations.

This invention further fulfills the above-described needs in the art byproviding a method of bulge testing a film at a plurality of differentlocations, the method comprising the steps of:

providing a bulge testing apparatus including a major surface and acavity defined therein;

providing a film on the major surface over top of the cavities;

evacuating the cavity so as to cause the film to deflect inwardly; and

measuring the deflection of the film caused by the evacuating, and basedupon the measuring determining modulus and stress properties of thefilm.

This invention further fulfills the above-described needs in the art byproviding a method of bulge testing a film, the method comprising thesteps of:

providing a bulge testing apparatus including a major surface and acavity defined therein;

providing a film on the major surface over top of the cavities;

allowing the film to bulge, either inwardly or outwardly, as a result ofinherent pre-stress present in the film, without pressurizing orevacuating the cavity; and

measuring bulging or deflection of the film caused by the pre-stress, sothat it is unnecessary to either pressurize or evacuate the cavity inorder to bulge test the film.

In certain preferred embodiments, a lookup table is stored in the systemwhich enables the system to determine, via the lookup table, theresidual stress of a film being tested in view of the film's measureddeflection, thickness, material, and the pressure applied in the cavity.The look-up table may utilize finite element analysis (FEA) to performthese functions.

Still further, this invention fulfills the above-described needs in theart by providing numerous specific methods for manufacturing membranestructures, which are discussed below.

This invention will now be described with reference to certainembodiments thereof as illustrated in the following drawings.

IN THE DRAWINGS

Prior art FIG. 1 is a side elevational view illustrating a thin filmattached to a mounting structure being deflected upwardly under theinfluence of pressure during a bulge test.

Prior art FIG. 2 is a schematic illustrating the vertical equilibrium ofthe film being tested in Figure Prior art FIGS. 3(a)-3(f) are sidecross-sectional views illustrating the manufacture of a membranestructure adapted to receive a thin film to be bulge tested.

Prior art FIG. 4 is a schematic illustration of a known bulge testingapparatus and system.

FIG. 5(a) is a schematic illustration of a bulge testing apparatus andsystem according to certain embodiments of this invention.

FIG. 5(b) is a graph illustrating the upward center deflection of thefreestanding flexible portion (e.g. circular-shaped) of a siliconmembrane, as a function of pressure, when tested in the FIG. 5(a) bulgetesting system.

FIG. 5(c) is a graph illustrating the upward center deflection as afunction of applied pressure, using the FIG. 5(a) system, wherein bothan uncoated silicon freestanding membrane portion (e.g. circular-shaped)deflection is illustrated as well as the curve for the same freestandingmembrane portion coated with a thin film to be analyzed.

FIGS. 6(a)-6(c) are side partial cross-sectional views illustrating howa membrane structure is manufactured according to an anodic bondingembodiment of this invention.

FIGS. 7(a)-7(f) are side partial cross-sectional views illustrating howa membrane structure is manufactured according to another embodiment ofthis invention, which utilizes a single crystal silicon wafer and doublediffusion of a vertically structured etch-stop into the substrate orwafer, and a chemical etch.

FIGS. 8(a)-8(e) are side partial cross-sectional views illustrating amethod of manufacture of a membrane structure according to yet anotherembodiment of this invention, utilizing a SIMOX wafer (or SOI—silicon oninsulator, wafer), and deep vertical etch.

FIGS. 9(a)-9(d) are side partial cross-sectional views illustrating themanufacture of a membrane structure according to still anotherembodiment of this invention, utilizing both a SIMOX (or SOI) wafer andanodic bonding.

FIGS. 10(a)-10(e) are side partial cross-sectional views illustrating amethod of manufacturing a membrane structure according to anotherembodiment of this invention, utilizing both anodic bonding and a singlecrystal silicon etched wafer.

FIG. 11 is an exploded perspective view illustrating a large areamembrane structure and corresponding mounting chuck according to anembodiment of this invention, this membrane structure including an arrayof separate and independent flexible freestanding membrane portionswhich allow the physical/mechanical properties of a film(s) to be testedacross substantially the entire surface/array of the membrane structure,or a portion thereof.

FIG. 12 is a perspective view illustrating a membrane structureaccording to an embodiment of this invention which is similar to theFIG. 11 embodiment, except that a different number and arrangement offreestanding flexible membrane portions are provided, and the method ofmounting and pressurizing the membranes is different.

FIGS. 13 and 14 are perspective views illustrating different channelarrangements for use with the bottom wafer of the FIG. 12 membrane arraystructure.

FIGS. 15-70 are schematic illustrations of system requirements forcomputer code used in bulge testing systems herein, according to anembodiment of this invention. These illustrations may be used by anyexperienced LabView programmer to develop preferred functionality anduser interface for the systems herein. The software, may be writtenunder LabVIEW Version 3.1 (National Instruments Corp.) running on MSWindows 3.1. It typically requires at least a 33 MHz or faster 486DXclass machine for consistent reliable operation. It has been run on a486DX/2 machine running at 66 MHz. Typically, RAM of at least 8Megabytes is needed, while conservative disk space requirements start atabout 5 Megabytes, depending on the duration of tests and the datastorage mode selected. The acquisition and control routines typicallyneed a Computer Boards Corp. data acquisition board and the associatedUniversal Library Software with LabVIEW extensions. The data acquisitionand control algorithms are based on LabVIEW from National InstrumentsCorp. In contrast to the text-based languages such as FORTRAN or C, thegraphical programming language called “G” uses block-diagrams togenerate applications. The appended documentation of FIGS. 15-70 ofconnector panes, front panels, controls and indicators, block diagrams,position in hierarchy, and sub VIs may be used by skilled “G”programmers, without undue experimentation, to duplicate thefunctionality and interface of the bulge test data acquisition andcontrol software in preferred embodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals indicate like parts throughout the severalviews.

Set forth below, and in the drawings, are numerous embodiments of ourinventions which relate to bulge testing techniques, test products, testtechniques, and methods of making and carrying out same. Bulge testingof films (including coatings and layers) such as those composed ofmetals (e.g. Ni, Cu, Ag, gold, aluminum, etc.), paint, dielectric thinfilms, organic compounds or polymers (e.g. photoresist), hard coatings,ceramics (e.g. ITO, silicon nitride, silicon carbide, etc.), and/or thelike, is a way in which to measure the film's mechanical properties, incertain embodiments in situ. The supporting membrane may be made, incertain embodiments, of any suitable material such as those discussedabove, but it is preferable that the membrane is of a material that isresidual-stress free, easily characterized, and easily made, such as,but not limited to, semiconductor grade single crystal silicon.

As pressure is applied to one side of a suspended thin film 57, disposedon a freestanding portion 68 of a membrane structure 47 in certainembodiments, the deflection of film 57 is measured as a function of theapplied pressure in cavity 53. Behavioral characteristics of film 57 area function of pressure load versus its deflection. The biaxial modulusand the residual stress of the film being tested can be determined fromthe relationship between the film's deflection and the applied pressureusing known mathematical techniques, as discussed above.

In alternative embodiments of this invention, the deflection of film 57and/or membrane portion 68 may be caused by pressure evacuation ofcavity 53, or even with no pressure or evacuation on either side of thefilm.

The bulge testing systems herein measure relative deflection of a film57 or membrane portion 68, with a resolution of better than 0.1 micronsand a differential pressure range from about 0.01 to 150 psi (with apressure resolution (or accuracy) of better than about 0.5% over thisrange). The preferred pressure applied to one side (top or bottom side)of a sample is from about 0-5 psi. This permits measurement of a numberof mechanical material properties, including elastic (e.g. residualstress, biaxial modulus), inelastic (yield strength, rupture strength,adhesion) and time-dependent (creep behavior, relaxation, fatigue,stress corrosion) properties. Additionally, automated measurement isprovided, precision of mounting membranes on mounting platforms orchucks is discussed, and array bulge testing capability is described.

In alternative embodiments herein, information regarding the rupture ofa membrane or film being tested may be gathered. For example, it can bedetermined at what point (with regard to deflection and/or pressure) aparticular film with a given thickness ruptures.

STRESS AND MODULUS

Residual stress is a significant characteristic in predicting mechanicalfailure or performance of films. Residual stress includes intrinsicstress, deposition induced stresses, and stress resulting frommismatches between thermal expansion coefficients of the film and acorresponding substrate. High residual stress can cause cracking andadhesion problems in films, and may also cause shape deformation ofcoated substrates. Other physical film properties are also affected byresidual stress.

Knowledge of elastic moduli of thin films is important for severalreasons. Elastic moduli are used to determine stresses in thin films.The elastic moduli provide an indication of the physical structure andcomposition of the film, for example, whether the film is crystalline oramorphous. Knowledge of the elastic moduli is necessary for anycharacteristic of a thin film, whether electrical, mechanical, orphotonic, that depends on the state of stress and/or strain. One way todetermine biaxial moduli of thin films is to measure thepressure/deflection characteristic of the thin film 57, either alone oras deposited on a membrane structure 47. Young's modulus can be obtainedfrom the biaxial modulus by knowledge or estimation of Poisson's ratio.

In bulge testing, when we measure the deflection of a membrane portionand thin film thereon as a function of the pressure applied to one sidethereof, we are measuring the stiffness characteristic of the film.Because we know the geometry (e.g. thickness) of the film being tested,the elastic modulus (i.e. Young's modulus) can be extracted. Note thefollowing exemplary equation:

Biaxial modulus (BM)=EM÷(1−v)

where “v” is Poisson's ratio, “EM” is the elastic modulus, and “BM” isthe biaxial modulus.

TESTING APPARATUS/METHOD

FIG. 5(a) hereto is a schematic illustration of an overall system usedfor bulge testing according to certain embodiments of this invention.The system includes mounting/alignment structure 45, membrane structure47 mounted on supporting structure or chuck 45, thin film 57 to beanalyzed disposed on membrane structure 47, transducer 49 for measuringthe deflection 50 of the flexible freestanding portion 68 of membranestructure 47 and/or thin film 57 to be tested/analyzed, pressurizationsystem 51 for applying fluid (gaseous or liquid) pressure within cavity53 and thus to the bottom side of flexible portion 68 of membranestructure 47, and data acquisition, analysis, and control system 55. Acomputer controlled XYZ stage upon which membrane structure 47 and thinfilm 57 to be bulge tested are mounted, and computer controlled pressureregulator and pressure sensor 51, are used to place freestandingflexible portion 68 of membrane structure 47 and thin film 57 throughpredetermined pressure cycles. The pressure sensor is in operativecommunication with cavity 53 (e.g. within the cavity) to monitorpressure therein.

For accurate testing, membrane structure 47 (including portion 68) ischaracterized alone via bulge testing so that thickness measurements,dimensions, and stand-alone bulge testing data can be taken whereby anyresidual stress, prior deflection, and other properties or responses aremore precisely known to the user before film 57 is applied thereon.Then, thin film 57 to be tested is applied to membrane structure 47 andbulge tested. Because the physical properties and characteristics ofmembrane structure 47 are known, the bulge test data can be used todetermine residual stress and elastic modulus characteristics of film 57via known mathematical techniques.

To measure the thickness of either the freestanding membrane film 68, orfilm 57, a mask or coating 90 (see FIG. 7(f)) can be in place on a smallportion of the wafer away from the freestanding portion duringdeposition, and then removed to lift off film 57 thereby creating a stepwhich can be used to measure the thickness of layer 57. The resultingstep surface may then be measured to determine the thickness of the filmat issue.

Preferably, optical displacement transducer 49 records either the center52 of deflection of film 57 or alternatively the center of the film overthe cavity relative to non-deflected points 54 spaced therefrom, as afunction of pressure. The maximum and minimum compliance which may bemeasured by the FIG. 5 system is determined by the resolution andmaximization capabilities of the pressurization system (i.e. regulator,pressure transducer, and control system), and deflection transducer 49.These values are variable, and should be chosen for the particularapplication to which the FIG. 5 system is to be applied. Additionally,the particular geometry of membrane 47 (and the film 57 to be tested)may be optimized for particular materials and mechanical properties ofinterest.

Pressurization system 51 preferably applies pressures from about 0 to 5psi to cavity 53, and transducer 49 measures membrane portion 68 andfilm 57 deflections of from about 0.01 to 1,500 μm (preferably fromabout 0.1-100 μm). Membrane compliance from about 0.002 to 75,000 μm/psi(preferably from about 0.02 to 100 μm/psi) may be measured. Test controland data analysis, in certain embodiments, are provided by PC compatiblecomputer system 55 with, for example, a 12 bit analog digital dataacquisition board.

According to alternative embodiments of this invention, cavity 53 may bede-pressurized or evacuated thereby causing freestanding membraneportion 68 and/or film 57 to bulge downwardly into the cavity. In suchembodiments, the downward deflection is measured and used to determinethe stress and modulus properties discussed herein.

In still other embodiments, cavity 53 is neither pressurized norevacuated, and the pre-stresses inherent in film 57 and/or portion 68cause it to bulge either outwardly or inwardly. This bulging may bemeasured by transducer via center point 52 relative to non-deflectedpoints 54, as discussed herein.

FIG. 5(b) is a pressure v. deflection curve for a silicon membrane 47,and illustrates that a well-characterized predictable membrane structure47 can act as a substrate for the evaluation of a number of differentthin film coatings 57. Thin films, layers, and coatings 57 herein aretypically from about 100 Å to 500,000 Å thick, preferably from about 100Å to 50,000 Å thick, and most preferably from about 500 Å to 5,000 Åthick. In certain embodiments, films or layers (e.g. paint) of evengreater thickness may be bulge tested. In a commercial setting, thissystem can measure residual stress of a film 57 within about ±5%accuracy.

FIG. 5(c) is a graph illustrating applied pressure (psi) v. center 52film deflection (μm) for both an uncoated stand-alone flexible membraneportion 68, and such a portion 68 coated with a thin film 57. A largeinitial deflection in the coated membrane (e.g. at 0 psi—0 psi appliedpressure) may be due to the high residual pre-stress introduced by film57.

The response of the flexible freestanding portion 68 of membranestructure 47 to pressurization in cavity 53 is a function of thegeometry and material properties of the membrane, and when applied, thethin film overcoat 57 to be measured.

In order to determine the mechanical properties of film 57 to bemeasured, the geometry of the membrane 47 must be precisely controlled,and measured or known prior to application of film 57, and the thicknessof the thin film 57 to be measured must be accurately determined. Avariety of manufacturing techniques are disclosed herein which have beenfound to create improved and more accurate and consistent membranestructures 47, these enabling the membrane structures to be uniformlycharacterized relative to one another.

Accurate mounting of membrane structure 47 on structure 45 is alsoimportant for reliable characterization and measurement. Membranestructure 47, and the thin film 57 to be measured and placed thereon,are originally held in place and hermetically sealed to the pressure (orevacuation) system. Furthermore, it is important that stresses not beintroduced to membrane structure 47 by the technique which is utilizedto attach the membrane to structure 45. Motion of membrane structure 47due to temperature changes, vibration, or poor fixation to structure 45is desired to be minimized. Additionally, flatness of the bond betweenmembrane structure 47 and structure 45 is important, and the alignmentof the membrane relative to structure 45 is done by scanning viatransducer 49, or alternatively by fabricating membrane structureshaving freestanding portions 68 exactly centered to their structure/chipshoulder 91 (see FIG. 7(f)), with the structure/chip then being placedinto a jig (not shown) exactly positioning the membrane portion 68centered relative to transducer 49. In some embodiments, fiduciary marksare applied to the membrane, or film 57, to enable efficient manual orautomatic orientation of the membrane portion 68 or film 57 in thesystem. In certain embodiments, membrane tructure 47 is attached to apressurization mounting chuck which functions as supporting structure 45and transducer uses the fiduciary marks on portion 68 or film 57 toaccurately position the center 52 of film 57 over cavity 53 directlybeneath the transducer.

In certain preferred embodiments of this invention, membrane structure47 is adhered or bonded to pressurization chuck 45 by way of CrystalBond™ polymer. Crystal Bond™ polymer, a mounting wax, which is availablefrom vendors of polishing supplies, such as Buehler, Ltd., Lake Bluff,Ill., as Part No. 408150. An important characteristic of this polymerbonding material is that it has a glass transition temperature above thetemperature at which bulge testing is usually performed. This polymeradhesive is heated above its rather low glass transition temperature(about 80° C.) to allow liquid flow into a thin layer. The mounting wax(e.g. element 200 in FIG. 6) has a wax or solid to liquid transitiontemperature of at least about 40° C., preferably of at least about 60°C., and most preferably at least about 80° C. Membrane structure 47 isthen placed onto this liquid polymer and upon cooling is fixed in placeon structure 45. Membrane structure 47 may be removed from structure 45by heating the mounting chuck to 80° C. or higher (and can be followedby rapid removal of residual Crystal Bond using acetone). Provided thatthe substrate of membrane 47 is sufficiently rigid, stresses introducedto the membrane by mounting are minimized when Crystal Bond™ is used. Itis noted that other polymers having characteristics similar to CrystalBond may also be used (e.g. having a glass transition temperaturegreater than temperatures at which bulge testing is typicallyperformed).

Epoxies and cyanoacrylate adhesives may alternatively be used to bondmembrane structure 47 to supporting structure 45, but these areundesirable in some circumstances because it is difficult to remove themembrane from structure 45. Without soaking the membrane and chuck insolvents such as acetone, dissolution is slow at best. These epoxies oradhesives cannot be removed by heating because they decompose and leavecarbonized residue rather than melting, and dissolution of epoxies oradhesives in solvents such as acetone is very slow, and tends to leave athin layer of organic reside which could alter the response of themembrane and impair thin film 57 analysis.

Optionally, mechanical clamping techniques may be used to connectsilicon based and metallic membrane structures 47 to mounting structure45. However, it is sometimes difficult to reproducibly clamp andhermetically seal membrane structure 47 to mounting structure 45. It isnoted that a rigid, stress free adhesion of membrane structure 47 tostructure 45 is important, as is the hermetic seal between 47 and 45.This, surprisingly, is best achieved with Crystal Bond™ or any othersuitable mounting wax, although alternatives are, of course,contemplated. For example, when it is undesirable to raise thetemperature above 80° C. or when simple adhesives are sufficient, epoxy,cyanoacrylate, or even simple mechanical clamping, may be used insteadof Crystal Bond™.

In certain embodiments, in order to ensure the top alignment plane ofmembrane structure 47 as being perpendicular to the vertical axis oftransducer 49, and the centering of transducer 49 relative to membranestructure 47, a computer controlled motion system is used. The precisionto which deflection transducer 49 is centered upon membrane structure 47(and/or film 57) is dictated by the sampling spot size and the curvatureof the membrane structure and/or film 57. Current laser triangulationsystems have spot sizes on the order of about 35 μm. Positioning oftransducer 49 in the center of membrane structure 47 and film 57 mayrequire incremental membrane motions which are achievable by standardand air bearing XY or XYZ stages with piezoelectric, stepper motorand/or brushless DC motor drive systems. During alignment, it isimportant that the translation stage being substantially free of pitch,roll, and yaw. The fiduciary marks also help substantially in alignment.Procedures for finding and centering a transducer on a membrane areuseful for arrays of membrane portions 68 as well, as the instrument canthen automatically move from portion 68 to portion 68 to makemeasurements.

Non-contact deflection measurement of freestanding portion 68 ofmembrane structure 47 and thin film 57 thereon, over a circular area onthe order of tens of microns with submicron resolution, is provided incertain embodiments. Ideally, the system remains relatively insensitiveto changes in surface finish due to coating application, and to loss ofintensity due to transmission through membrane 47, and/or thin filmcoating 57 thereon. The radiation used by transducer 49 for measurementtypically does not excite any response in membrane structure 47, or thethin film coating 57 thereon, which may alter the response of themembrane. It is still possible to achieve measurements with interaction.Furthermore, deflection measurement device 49 samples a small enougharea of portion 68 of membrane structure 47, and thin film coating 57thereon, so that the local radius of curvature of the surface of portion68 and film 57 does not introduce significant or substantial error intothe measurement. When measuring deflection, in certain embodiments, thedeflection of the center 52 of the thin film coating 57, on orindependent of membrane portion 68, is measured relative tonon-deflected edges 54 of the membrane, non-deflected points 54 beingspaced from cavity 53. Simple measurement of the center-52 is not alwayssufficient. Thus, at a minimum, where resolution dictates, threemeasurements are utilized—the center point 52 deflection of thin filmcoating 57, and a pair of non-deflected opposite points 54 on the edgeof the membrane structure. Referring to FIG. 1, this type of measuringusing the deflection of the center 54 of the film relative tonon-deflected edge points 54 can be easily illustrated, with the apex ofthe bulging film in FIG. 1 being the deflected center 52 of the film andthe non-deflected edge portions/points 54 being on the two parts of thebulging film that are not over the cavity and which are not deflected.

Accordingly, another embodiment of the deflection measurement devicesaccording to this invention, measures a section of the deflectedmembrane profile, or the entire profile, or the entire three-dimensionalshape of the membrane. This may be accomplished using profilometrysurface analysis systems such as laser triangulation or white lightinterferometry. The advantage of this embodiment is that it measures thecenter deflection (at a center point 52) relative to points 54 on theundeflected edges of the substrate. The necessary information includesthe center deflection, measured relative to two points 54 on thesubstrate which define a line that substantially bisects or crossesmembrane portion 68. The additional information provides additionalaccuracy.

TABLE 1 Displacement Transducer Models Manufacturer Model DescriptionLucas Control Schaevitz Laser Systems TwinStar 15/3 triangulation sensorPhiltec, Inc. Model D6L Fiber optic displacement sensor Zygo, Inc. NewView 2000 Scanning white Non-Contact light Surface Structureinterferometer Analyzer

Different approaches may be used to measure deflection of thefreestanding flexible portion 68 of the membrane, and overlying film 57,without mechanical contact therewith. For example, in certainembodiments, electrical methods based upon capacitive and inductiveschemes may be used. Also, acoustic-ultrasound may be used to measuredeflection, as may contact probe systems. Also, electron tunneling maybe used to measure deflection. However, such electrical methods are notpractical for use with all membrane and thin film materials of interest.Alternatively, variable induction deflection measurement systems havingspot sizes on the order of about 2 mm, may be used, but are too largefor many membrane designs. Still further, atomic level measurementtechnologies such as atomic force microscopy (AFM) may be used tomeasure local deflections of membrane portion 68 and coating 57, butthese are limited to small areas and deflections.

Optical techniques are preferred for measuring deflection of film 57 andthe flexible freestanding portion 68 of membrane structure 47, andprovide a wide variety of approaches to non-contact displacementmeasurement. Typically, optical techniques for deflection measurement bytransducer 49 are based on monochromatic light sources with theexception of white light interferometry. Interferometric, reflectionprobe, laser focusing, and laser triangulation systems provide viableoptical deflection measurement transducers 49.

Interferometric measurement systems based upon HeNe lasers, whilecostly, may also be used for precision distance measurement in order todetect the bulging or deflection of portion 68 and/or film 57. However,it is noted that the HeNe laser light may experience transmissionthrough silicon. White light interferometry (or interferometers 49) maybe used for surface profiling of freestanding portions 68 and films 57,relative to the surrounding substrate. Reflection probes may also beused to measure deflections of the freestanding portion 68 of membranestructure 47, and/or film 57, although these sometime suffer fromsensitivity to changes in surface roughness, reflectivity, andtransmission through silicon. In another preferred embodiment, a lasertriangulation transducer 49 is used for characterizing membranestructure 47 and coating 57 surfaces, and center 52 deflection relativeto edges 54 thereof.

It has been found that the use of stored lookup tables is surprisinglyuseful in the determination of film (thin films, coatings, layers, etc.)properties herein. For example, computer-controlled system 55 may havestored therein (e.g. stores in a RAM or ROM) a lookup table which, foreach potential thin film material 57 or membrane portion 68 to betested, includes potential thicknesses and measured deflections atparticular pressures or evacuation, and a resulting stress value (e.g.residual stress). For example, such a lookup table may include two axes,an X axis and a Y axis, wherein the Y axis defines different thicknessesof a given material to be bulge tested, and the X axis includes aplurality of potential measured deflections at different pressures thatare measured via transducer 49. Thus, when the system measures aparticular deflection, the lookup table for that particular materialbeing is tested may be accessed, and because the thickness and materialof the film being bulge tested is known, it is possible from the lookuptable to determine the precise residual stress. For example, if analuminum thin film 3,000 Å thick is bulge tested, and a deflection of5,000 Å is measured, then an aluminum film lookup table stored in thecomputer is accessed and when the thickness of the film is matched upwith its measured deflection and pressure applied, the lookup table willindicate a predetermined residual stress (or other stress or propertyvalue) of the film. A different lookup table may be provided in thesystem for each material, or alternatively, one large lookup tableinclusive of all potential materials which may be tested can beprovided.

Pressurization system 51 applies a known pressure or pressurizationprofile. The application of gas into cavity or chamber 53, in certainembodiments, is such that membrane structure 47 is not adverselyaffected by the gas, and temperature fluctuations of significance do notoccur so that membrane 47 is relatively stable. In certain embodiments,special reflective or opaque coatings (e.g. gold, aluminum, platinum,etc.) can be placed over or on film 57 to facilitate optical measurementof deflection.

Set forth below in Tables 2 and 3 are different exemplarycomputer-controlled pressure regulators which may be utilized accordingto different embodiments of this invention in order to detect thepressure being applied to the lower side of membrane portion 68 viacavity 53.

TABLE 2 E/P and I/P Transducers (computer-controlled pressureregulators) Company Name Model Comments Proportion QB1T Servo QB1TFEE0050-5 psi Air Control output, 0 to Valve 10 V FS Bellofram Type 1001966-210-000 0-5 psi E/P output, 0 to Transducer 10 V FS Tescom ER3000ER3000S-A001 0-5 psi Electronic output Pressure Controller

TABLE 3 Electropneumatic Transducer Technical Specifications ProportionTescom Air Bellofram (ER3000S- (QB1TFEE005) (966-210-000) A001) SupplyVoltage 15-24 V DC 9-40 V DC 19.5 to 28.5 V DC Supply Current 250 mA maxCommand Signal Voltage 0-10 V DC 0-5 V DC 1-5 V DC Current 4-20 mA 4-20mA 4-20 mA differential Command Signal Impedance Voltage 4700 Ω 6000 ΩCurrent 100 Ω Analog Monitor Signal Voltage 0-10 V DC none 1-54 V DCCurrent 4-20 mA 4-20 mA sinking Pressure Range 0-5 psi 0-5 psi 0-5 psiCv Capacity 0.04 0.01 Linearity/ +−0.15% FS 0.01% span Hysteresistypical, 0.10% span max Repeatability +−0.02% FS 0.01% span, typical,0.10% span max Accuracy +−0.2% FS per ISA 51.1 +−0.1% span typical,+−0.25% span max Operating 0-70 C. −20 to 160 F. Temperature VibrationEffect Less than 0.5% of span per 1G, 5-2000 Hz, 3G maximum, 3 axes

A differential pressure transducer is typically used to determine thepressure applied to membrane portion 68. Due to low pressures used inthe system, daily fluctuations in atmospheric pressure may be anappreciable fraction of the applied pressure and differentialmeasurements must be made. Silicon diaphragm and bonded strain gaugepressure transducers are both viable technologies for this application.

In preferred embodiments, clean, low moisture, compressed gases are usedas the pressure medium for applying pressure through regulator 51 intocavity 53. Failure to control the purity of the gas may result incorrosion of the system. Exemplary gases for applying pressure in cavity53 include nitrogen, dry air, He, and/or argon.

MEMBRANES

It has been found that the membrane structures 47 discussed below, andtheir methods of manufacture, are improvements over the prior art withrespect to efficiency, durability, and/or manufacturability topredetermined tolerances. This allows the instant inventions to becommercially viable. These membrane structures 47 and/or methods ofmanufacture enable mass production of such membranes to a predeterminedfinite tolerance value, ± about 5%, preferably within about ±3%, and insome cases about ±1%. In other words, for example, it has beensurprisingly found that if a manufacturing process described below isused to make one hundred membrane structures 47, at least about 95% ofthe resulting membrane structures would have the same thickness ± about5% (preferably ± about 3%, and most preferably ± about 1%) offreestanding portion 68, and in circular embodiments the same diameter ±about 5% of portion 68 and cavity 53. For example, if a thickness ofabout 1000 Å is desired, at least about 95% of the resulting membranestructures will have a portion 68 having a thickness within about 5% of1000 Å (i.e. a thickness of portion 68 of from about 950 to 1050 Å), andpreferably a thickness within about 3% of 1000 Å (i.e. a thickness ofportion 68 of from about 970 to 1030 Å), and most preferably a thicknessof within about 1% of 1000 Å. This is important for commercialimplementation of bulge testing.

Preferably, freestanding membrane portions 68 are made of single crystalsilicon which is reproducible into a geometric shape in mass numbers(e.g. substantially the same thickness and diameter of portion 68 can beachieved time after time). Although not preferred, silicon nitrideand/or silicon oxide may be used to form portion 68 in alternativeembodiments. optionally membrane portions 68 in any of the structures 47discussed herein, of varying thickness or in-plane geometries, may beused to evaluate different properties such as Poisson's ratio or tofacilitate the measurement of tensile stresses through induced buckling.

Membrane structures 47 and/or freestanding portions 68 may be eithercircular or square in shape according to different embodiments of thisinvention. Circular membranes often render measurements insensitive toanisotropy, while square or otherwise rectangular membrane structurespermit the detection of anisotropy. Both have advantages in differentapplications. Accordingly, while circular membrane portions 68 arepreferred in certain embodiments, both may be manufactured and used inall embodiments herein.

Generally speaking, the freestanding thin film membrane portions 68herein are from about 500 Å to 15 μm thick, and preferably from about500 Å to 10 μm thick.

A first type of membrane structure 47 shown in FIG. 6(c) is manufacturedwith a pyrex glass substrate 61 and anodic bonding. Referring to FIGS.6(a)-6(c), pyrex glass substrate 61 is provided as shown in FIG. 6(a).Cylindrical or circular hole(s) 63 are then defined (e.g. drilled orultrasonically machined) in substrate 61 [see FIG. 6(b)]. Hole(s) 63 inglass substrate 61 may have a diameter of from about 0.5-20 mm,preferably from about 1.0-10.0 mm, and most preferably from about2.0-5.0 mm. A thin single crystal silicon film 65 about 9 μm thick isthen bonded to the top surface of glass substrate 61 by anodic bondingin order to form freestanding membrane portion 68. When anodic bondingis used herein, voltage (e.g. 600 volts DC bias) and temperature on theorder of about 300 degrees C. or higher are used across silicon 65 andglass 61 to bond the glass to the silicon. An exemplary silicon layer orfilm 65 can be purchased from Virginia Semiconductor, who produces verythin single crystal silicon wafers which may be used as film 65.

The resulting FIG. 6(c) membrane structure 47 may then be bonded tomounting structure 45, and thereafter a thin film 57 to be analyzeddeposited or otherwise disposed on the membrane's top surface over layer65 and cavity 53. The only portion of the FIG. 6(c) membrane structure47 that is susceptible to bulging during bulge testing is thefreestanding flexible membrane portion 68 that covers drilled hole(s) 63(and cavity 53).

In certain embodiments, Virginia semiconductor can provide siliconwafers 65 having about a 2″ diameter, about 9 μm thick with flatness 3,planarity 3, and taper of about 2.5. The thickness of layer 65 (and thusfreestanding portion 68) is preferably from about 500 Å to 15 μm incertain embodiments herein (most preferably from about 1 μm to 15 μmthick), while the thickness of glass 61 in the FIG. 6 embodiment ispreferably from about 0.075 to 0.250 inches, most preferably about 0.125inches.

In certain other embodiments, a double diffusion technique is used tomanufacture membrane structures 47, as illustrated in FIGS. 7(a)-7(f).Firstly, a first area of the top surface of single crystal silicon wafer71 is covered with circular mask 73 as shown in FIG. 7(a). Other shapedmasks may also be used (e.g. oval, square, etc.). Then, using mask 73,the top surface 74 of wafer 71 is exposed to deep diffusion 77 (orimplant followed by deep diffusion) with an etch stopping material inthe area not covered by the mask, as shown in FIG. 7(b). Mask 73 is thenremoved. Then, as illustrated in FIG. 7(c), another mask 75 is depositedor provided on a second area which had previously been doped by deepdiffusion. Alternatively, the second mask need not be used, and the topsurface may simply be exposed to shallow diffusion, or implant followedby anneal giving shallow diffusion depth to a predetermined membraneportion 68 thickness depth as shown in FIG. 7(d). The first and secondareas discussed above preferably slightly overlap, but need not. Thediffusion depth in the FIG. 7(d) step is less than the diffusion depthin the FIG. 7(b) step. The difference between this predetermined FIG.7(d) depth and the depth of diffusion in the FIG. 7(b) step, accountsfor step 79 between these two depths or areas. The timing employed inthe FIG. 7(d) step is important to obtaining a reliable predeterminedflexible membrane portion depth which is defined by the thickness ofdiffusion 81. The diffusion steps discussed above in applying etch stopto the first and second areas may be conducted in either order.

Following the FIG. 7(d) step, the backside 83 of wafer 71 is masked asillustrated in FIG. 7(e) at 85, for an anisotropic etch in basic(caustic) etchants of the class KOH, EDP, TMAH, etc. Thereafter, asillustrated in FIG. 7(f), the backside of wafer 71 is anistropicallyetched to form the freestanding flexible portion 68, 87, of the membranestructure 47. The etch can be KOH, EDP, TMAH, or other known etchingagents that employ an etch stop. The resulting FIG. 7(f) membranestructure 47 may be used in bulge testing embodiments of this invention.Membrane structure 47 includes thin freestanding membrane area 68, 87upon which the thin film 57 to be bulge tested and analyzed isdeposited. Flexible freestanding portion 68, 87 of membrane structure 47is surrounded by thicker non-flexible membrane portions 89 that wereformed as a result of the etch stop provided in the FIG. 7(b) step.Shoulder(s) 91 of silicon wafer 71 remain so as to allow membranestructure 47 to be adhered to the mounting structure to form cavity 53.

According to other embodiments of this invention, membrane structure 47is formed by way of a SOI method using a silicon-on-insulator wafer, asillustrated in FIGS. 8(a)-8(e). In the method, a wafer 101 prepared withby the SIMOX method, or a SOI method, is provided, e.g. as shown in FIG.8(a) (including four layers in this particular embodiment). For example,SIMOX wafer 101 may be obtained from Ibis Corporation, or alternativelyfrom Nippon Steel. Wafer 101 includes an embedded oxide layer 107 abovea single crystal silicon insulating layer 99. Epitaxial growth ofsilicon onto the oxide layer is used to increase the thickness of thesilicon layer to that which is desired. These SIMOX wafers may havetheir single crystal silicon layer from about 1.0 to 20.0 μm thick,preferably from about 6.0-10.0 μm thick, depending upon the mechanicalproperties and thickness of the film being measured. The layers of wafer101 are oxide layer 111, epitaxial silicon layer 110, oxide layer 107,and silicon insulating substrate 99. Top oxide layer 111 is optional,and is not needed in certain embodiments. Layer 111, whether siliconoxide or some other material, may optionally be deposited/grown onto Silayer 110, 68 to protect it during subsequent processing.

Following the provision of SIMOX wafer 101, mask 103 (e.g. photoresist,patterned silicon oxide, etc.) is applied to the backside of the waferas illustrated in FIG. 8(b) to expose an area which is to define cavity53. As in FIG. 7, mask 103 is annular with a circular opening 105provided at its center so as to expose central surface area on thebackside of the wafer. Following masking, in FIG. 8(c), deep reactiveion etching (RIE) is performed from the backside of the wafer, thisetching stopping at SiO₂ layer 107 which functions as an etch stop. ThisRIE step in FIG. 8(c) forms circular aperture or cavity 109 in wafer101, which finally ends up defining cavity 53 when the membrane isaffixed to structure 45. Then, as shown in FIG. 8(d), mask 103 isstripped off of the backside of the wafer. The optional top siliconoxide layer 111 is then stripped off of the wafer so as to form flexiblefreestanding portion 68 of membrane structure 47, with a thin oxideunderlayer as illustrated in FIG. 8(e). Oxide layer 107 may be removedin cavity 53 via etching or the like in certain embodiments. The FIG.8(e) membrane structure 47 may then be adhered to mounting structure 45by way of an adhesive (e.g. Crystal Bond™) as discussed above. A thinfilm 57 (illustrated in FIG. 8(e) in dotted lines) is thereafter appliedto the top surface of the FIG. 8(e) membrane structure so that it can bebulge tested as discussed above.

Membrane structures produced using the FIG. 8 embodiment generallyproduce more flat portions 68 than process using anodic bonding becauseelevated temperatures of the anodic bond tend to introduce non-uniformstress between the two wafers after bonding and cooling to roomtemperature. However, this can be minimized by accurately controllingthe bond temperatures and tailoring the glass composition to match thethermal expansion coefficient of Si.

According to another embodiment of this invention illustrated in FIGS.9(a)-9(d), membrane structure 47 may be made using both anodic bondingand a SIMOX wafer as discussed above. In preferred embodiments, layer111 is not provided in the FIG. 9 embodiment herein. In FIG. 9(a), SIMOXwafer 101 is flipped upside down relative to its orientation in FIG.8(a). Then, as shown in FIG. 9(b), a substantially planar pyrex glass(or other glass composition having a thermal expansion coefficientsubstantially matched to Si to allow anodic bonding) slide, wafer, disk,or substrate 123 (e.g. about 0.63″ thick) is drilled with a circularhole(s) 121 (e.g. about 3.47 mm diameter hole(s)). One hole 121 isdrilled in pyrex substrate 123, unless a plurality or an array of thinfilm membrane areas are to be formed on the substrate, or unless themanufacturing technique involves forming a plurality of holes 121(equivalent to 63) in a large area substrate 123 and thereafter cuttingup same into a plurality of different membrane structures.

Thereafter, as shown in FIG. 9(c), the drilled pyrex substrate 123(equivalent to 61) is bonded to the oxide layer side of SIMOX wafer 101using anodic bonding or the like. Then, as shown in FIG. 9(d), the mainsilicon insulating body of the wafer is removed along with the lastsilicon oxide layer of wafer 101, thereby forming the membrane structure47 of FIG. 9(d). In preferred embodiments, layer 111 is not provided inthe FIG. 9 embodiment, so that freestanding membrane portion 68 includesonly silicon layer 110 in FIG. 9(d).

Also, the silicon substrate 99 can also be dissolved away, for example,in 25% TMAH (tetramethyl ammonium hydroxide) a 80° C. down to the buriedSiO₂ layer which serves as an etch stop. The silicon bonded over hole(s)121 may be protected from the TMAH with “black wax” or other polymerfilm(s).

The FIG. 9(d) membrane structure 47 includes a pyrex shoulder area 125surrounding cavity 53 which is preferably annular. The top surface ofmembrane structure 47 includes both the upper silicon layer, andoptionally even the second SiO₂ layer 107 in some embodiments. Membranestructure 47 is then bonded to is mounting structure or chuck 45, and athin film(s) to be bulge tested is placed on the upper surface of themembrane. The only portion of membrane structure 47 designed to “bulge”during testing is the flexible freestanding film/membrane portion 68covering the drilled hole(s). Because the manufacturing techniquedescribed herein to make structure 47 are so accurate, the geometry andresponse characteristics, and stresses, of structure 47 are known. Thus,film 57 can be applied over portion 68 without having to separatelybulge test each structure 47.

Exemplary SIMOX wafers herein available from IBIS Technology Corp., havea silicon layer 110 thickness of about 190 nm, have a wafer Siuniformity of plus/minus about 5 nm, a buried oxide (BOX) thickness ofabout 380 nm (preferably from about 100-500 nm), a pinhole density ofless than about 0.1 per cm², and metallics (TXRF) of less than about5×10¹⁰ cm². Also available are similar SIMOX wafers from IBIS undertheir trademarks ULSI and ADVANTOX⊥. The SIMOX layers 110 herein arefrom about 100 nm to 500 μm thick, preferably from about 100-250 nmthick, and most preferably from about 170-200 nm thick. SIMOX membranestructures 47 in SIMOX embodiments generally produce a more flat uppersurface than do simple silicon wafer embodiments. SIMOX wafers with Silayer 68 increased in thickness by epitaxial growth produce membraneswith less variation in membrane thickness for individual membranesproduced from one wafer, as compared to membranes produced by wafer bondand etch back SOI.

According to another embodiment of this invention shown in FIGS.10(a)-10(e), membrane structure 47 is formed by an anodic bondingprocess using single crystal silicon wafer 131. In this embodiment, thetop of silicon wafer 131 is doped with etch stopping material 132 asshown in FIG. 10(a) to a predetermined desired depth. Thereafter, theback side of the wafer is masked 133 (FIG. 10(b)) and a protective layertypically placed on layer 132, and the wafer anisotropically etched asshown in FIG. 10(c) to produce a square flexible freestanding membraneportion 68, 135, and a square cavity in the wafer surrounded by shoulderarea 134, the thin flexible freestanding membrane portion 68, 135 havinga thickness corresponding to the depth of the doped silicon. Referringto FIG. 10(c), a protective layer (not shown) is typically placed onlayer 132 across most of its upper surface during the etch process oflayer 131, with this protective layer then being removed prior to theFIG. 10(e) bonding step. Because of the etch stopping area 132, theetching cannot penetrate all the way through the wafer, but stops atlayer 132 thereby leaving the flexible membrane portion 68, 135. Then, apyrex.glass substrate 136 (equivalent to 61) is drilled with circularhole(s) 137 (equivalent to 63), and the etched silicon wafer is flippedand bonded to the drilled pyrex substrate 136 via anodic bonding asshown in FIG. 10(e) to form membrane structure 47.

According to other embodiments of this invention, membrane structure 47may include an aluminum foil thin film anodically bonded to a drilledpyrex glass substrate. For example, a 5 mm thick aluminum film may beanodically bonded to such a pyrex glass substrate having a thickness ofapproximately 0.125″, with drill hole(s) in the pyrex having a diameterof approximately 3.47 mm.

In some embodiments, a large area glass substrate may be provided anddrilled with an array of holes, and thereafter diced or cut up into aplurality of squares in order to form different membrane structures 47.To help dice or separate such a structure into different pieces, scribeor separation lines may be provided on the wafers to facilitate theproduction of individual membranes. These diced up pyrex glass chips orsquares may then be placed upon the aluminum foil with an anodic bondbeing formed at about 300° C. and about 1,200 volts DC bias, with thenegative electrode applied to the pyrex.

According to still further embodiments, a membrane structure 47 may beformed of a stainless steel thin foil sheet, coated with a polysiliconlayer, and anodically bonded to a pyrex glass substrate where thepolysilicon layer forms an anodic bond with the pyrex (or other glass).Also, the membrane structure may be made from other materials amenableto anodic bonding.

It is noted that each of the membrane structures 47 discussed above (seeFIGS. 6-10), can serve two different purposes. Firstly, the membranestructure 47 itself may be subjected to bulge testing in the FIG. 5(a)system in order to determine the characteristics and/or properties ofthe freestanding flexible film portion(s) 68 that covers the cavity.Thus, the stress and modulus characteristics of the flexible membraneportion 68 may be determined. The second use for each membrane structure47 is to serve as a base or supporting structure upon which a thin film57, which is to be analyzed, is deposited or otherwise disposed. Forexample, the FIG. 6(c) membrane structure 47 may be used as a base for athin film polymer coating (e.g. photoresist) which is to be analyzed. Insuch as case, the thin film photoresist polymer coating 57 (preferablyfrom about 500 Å to 5,000 Å thick) would be applied to the top surfaceof silicon (or other appropriate material) layer 65 of the FIG. 6(c)membrane structure so as to cover portion 68. When the overall structureincluding 47 and 57 is bulge tested in the FIG. 5(a) system, bothflexible portion 68 of layer 65, and the corresponding portion of theovercoating polymer layer 57 are caused to bulge due to either pressurewithin cavity 53, or the cavity being evacuated. For example, see the“coated” graph in FIG. 5(c). In this way, given the prior knowledge ofthe characteristics and properties of layer 65 and portion 68, thestress and modulus characteristics of the thin film polymer overcoat 57can be determined.

ARRAY MEMBRANE STRUCTURES

Each of the membrane structures 47 described above and illustrated inFIGS. 6-10 includes a single freestanding flexible membrane portion 68which is exposed to pressure or evacuation for causing bulging ordeflection. As discussed in the Background Section above, this does notenable one to determine the properties of a thin film, at differentlocations, across the surface area of a large substrate which is coatedwith the thin film. Accordingly, we have developed arrayed membranestructures 47, discussed below, which enable the testing and analysis ofa thin film(s) at different locations across a large surface area of anunderlying substrate.

FIG. 11 is a perspective view of an arrayed membrane structure 47 andcorresponding mounting structure 202 according to one embodiment of thisinvention. This structure may, of course, be used within the FIG. 5(a)bulge testing system, where the XYZ stage is manipulated bycomputer-controlled system 55 so that transducer 49 can measure theamount of deflection for each individual stand alone flexible membraneportion 68, and optionally its overcoat thin film 57 in the array.

Still referring to FIG. 11, an array of eleven (although any number maybe provided) different stand alone flexible membrane portions 68 aredefined on the top surface of structure 47. Any of themembrane-structures 47 illustrated in FIGS. 6-10 may be utilized in theFIG. 11 embodiment to form the array of flexible portions 68. Forexample, using the FIG. 6 type of membrane structure as an example, thearrayed membrane structure 47 in FIG. 11 may include an array of FIG.6(c) type membrane structures, where a pyrex glass substrate 61including eleven different apertures or holes 63 are drilled therein,and a flexible membrane portion 68 is provided over top of each of theseeleven holes 63 due to a thin silicon layer 65 being applied across theentire surface area of substrate 61. Thus, in this example, layer 201 ofthe FIG. 11 membrane structure 47 would represent an arrayed glass pyrexsubstrate 61 with the plurality of holes 63 defined therein, while layer203 would represent the silicon coating 65 applied over the array ofholes 63. The silicon coating 65 applied over the array of holes 63forms the array of flexible membrane portions 68 which can be bulgetested.

As can be seen in FIG. 11, given arrayed membrane structure 47, there isrequired a special mounting chuck 202 which takes the place of mountingstructure 45 illustrated in FIG. 5(a). Mounting chuck 202 in the FIG. 11embodiment includes at least a single pressure inlet aperture 204, aswell as an array of holes or apertures 205 which correspond to the arrayof flexible membrane portions 68 in membrane structure 47. Thus, whenmembrane structure 47 is adhered to mounting chuck 202 via CrystalBond™, (or some other rigid bond) pressurized gas is introduced intoaperture 204 and flows, via hidden channel passageways defined in chuck202, into each aperture 205 in the array thereby causing each flexiblemembrane portion 68 to bulge outwardly. Thus, the array of pressureapertures 205 in mounting chuck 202 allows pressurized fluid (e.g. gas,air, or liquid) to be applied to the underneath side of each flexiblemembrane portion 68 in the membrane structure thereby allowing bulgetesting to be performed. Optionally, each cavity 53 in the array may beevacuated by applying a vacuum to aperture 204, in order to cause thefilms to bulge inwardly.

Following the determinations of the characteristics of flexible membraneportions 68 in the array via bulge testing, a thin film 57 may beapplied or deposited across the entire top surface of the FIG. 11membrane structure 47 either continuously or in a segmented manner,thereby covering at least some, if not all, of the arrayed membraneportions 68. Structure 47, with its overcoating 57, is then bulge testedin order to determine the stress and modulus characteristics of thinfilm 57 across a large surface area of the arrayed. structure 47covering a plurality of portions 68. In such a manner, not only is itpossible to determine stress and modulus characteristics of thin film 57at the center of array structure 47, but it is also possible todetermine those same characteristics at the sides, edges, and otherareas across the structure. This enables a user or operator todetermine, for example, stress and modulus characteristics of a thinfilm that is deposited over a large surface area of a substrate, atdifferent locations thereon. This, of course, is useful for measuringthe uniformity of application of processes used to deposit a film(s) ona substrate. Also, a user could position strips or segments of differentfilm 57 materials over different arrayed portions 68 so as to determinethe characteristics of each such material over a large surface area.

FIG. 12 illustrates an arrayed membrane structure 47 according toanother embodiment of this invention. In this embodiment, membranestructure 47 includes an arrayed top wafer or member 221 having an arrayof flexible membrane portions 68 defined therein, and bottom sealingwafer or member 222. Top member 221 and bottom member 222 are preferablyrigidly coupled together in a hermetically sealed manner, with bottommember 222 being coupled to the mounting chuck in the same type manner.

Sealing wafer 222 has a single (or multiple) fluid inlet aperture(s)defined in a bottom surface thereof which allows pressurized gas,liquid, or air (or instead a vacuum to be applied) to flow into achannel system within structure 47 so as to selectively orsimultaneously pressurize (or instead evacuate) the underside of eachflexible membrane portion 68 in the array.

As illustrated in FIG. 13, sealing wafer 222 may have a singlepressurized inlet port 204 which is connected to (e.g. continuously), orin communication with, each flexible membrane portion 68 via acorresponding cavity 53. Fluid channel system 223, which is provided inthe FIG. 13 bottom sealing wafer 222, enables pressurized gas or liquidwhen inserted via aperture 204 to make its way to each of apertures 225.Each aperture 225 corresponds with, and is in communication with, acavity 53 of a particular flexible membrane portion 68, so thatpressurized gas from an aperture 225 causes the corresponding flexiblemembrane portion 68 to bulge. This bulging is outwardly towardtransducer 49 in pressurizing embodiments, and inwardly toward thecavity in evacuating embodiments.

In the FIG. 14 embodiment of bottom sealing wafer 222, three separatepressurized inlet apertures 204 are provided. This enables apertures 225and corresponding flexible membrane portions 68 in the array to beselectively pressurized, one row at a time. Also, the system can bedesigned so that one quadrant of the wafer can be selectively addressedat a time, and the like. Thus, pressurized gas may be applied to onlyone of the three inlet apertures 204, which results in only one row offlexible membrane portions 68 (and overcoated film(s) 57) being exposedto pressure and bulged. In a similar manner, it is possible to arrangethe pressurized channel system, and the number of inlet apertures 204,in bottom wafer 222, 50 that each flexible membrane portion 68 (andoverlying film 57) in the membrane structure array is individuallyselectively accessible. In such a manner, a user may selectively addresseach portion 68 in the array, one at a time.

COMPUTER PROGRAMMING/SOFTWARE

FIGS. 15-70 herein illustrate system requirements and computer code foruse in certain embodiments herein. Set forth below is a description ofthe operation of same.

Introduction: This documentation describes the operation of the LabVIEWMembrane Pressure Ramping Data Acquisition and Control Code. It alsodiscusses the internal operation of the code. Additionally, associatedutility programs are briefly discussed. The first section of thisdocument should be read before attempting operation of the system.

System Requirements: This software was written under LabVIEW Version 3.1running on MS Windows 3.1. Preferably, a 33 MHz or faster 486DX classmachine is used for consistent reliable operation. It has been run on a486DX/2 machine running at 66 MHz. Require RAM for operation is 8Megabytes, while conservative disk space requirements start at about 5Megabytes, depending on the duration and number of tests. The controland acquisition routines require a Computer Boards Corp. dataacquisition board and the associated Universal Library Software withLabVIEW extensions. The proper functioning of the board must beconfirmed before running tests, as this software has no means to detectimproper operation and must accept nearly all input as valid.

Operation: This section describes system operation, the front panelinterface, and the meaning and use of each control.

Operational Overview: The overall acquisition and control strategy usedin this system is extremely simplistic, but with many built-insafeguards and error correction mechanisms. At runtime, a number ofcontrol data structures are initialized, and the hardware interface(Computer Boards Hardware) are enabled and initialized. The user isprompted to enter file names for data storage. If these initializationsare successful (or the operator tells the system to ignore errors), themain control loop is entered. In this loop, the system reads the inputarrays of time and pressure targets, and divides the time and pressureaxes into equally spaced, small, discrete steps, and then walks throughthese steps and attempts to follow the steps to apply the desiredpressure profile. At each step, the actual pressure and deflection areread by the hardware, displayed on the panel. When the final check-pointis reached, the pressure is released, and the data and control buffersare transformed to disk. The test hardware is shutdown, disabled andreturned to a user controllable configuration.

Front Panel Interface: The front panel consists of a number of standardLabVIEW controls and indicators. The following sections detail thecontrols on the front panel.

Pressure Range: Sets the appropriate valves and enables the correctregulator for operation in both high (e.g. 0-5 psi) and low (e.g. 0-1psi) pressure ranges.

Displacement Sensitivity: Sets the sensitivity level of the displacementsensor in micrometers per millivolt.

Curvature Correction: Sets the second order correction value used tocorrect the displacement value for the curvature of the membrane whileunder pressure; the value should be entered in micrometers per millivoltper psi.

Time and Pressures: Arrays that allow the user to set the target timesand pressure for the desired pressure ramping profile.

The following are the indicators which return values to the user.

Start Time: Displays the start time for this program run.

Elapsed Time: Displays the current elapsed time for this program run.

Datafile Name: Displays the file name the current data run will bestored in.

Measured Pressure: Graphical display of the measurements of the appliedpressure profile for comparison to the desired profile.

Measured Deflection v. Pressure: Graphical display of the correctedmeasured deflection v. measured pressure profile.

Measured Deflection v. Time: Graphical display of the corrected measureddeflection v. time.

Internals: This section describes the internal details of theprogramming, including the operation of the main program, andsubsequently, of all the subroutines written for this program. Aknowledge of LabVIEW programming is required for a thoroughunderstanding of this section.

Overview: System execution consists of three main

phases: initialization, loading and acquisition, and shutdown. Themajority of the system's run time is spent in a main loop which enclosesthe loading and acquisition algorithms.

Initialization: During initialization, the Computer Boards acquisitionand control board is enabled and the ports are set appropriately forinput and output as necessary. The pressure regulators are set to zero.Empty arrays are initialized for the immediate storage of the datadisplayed in the three graphs on the front panel (“Initialize Array”function). The user is prompted for a file name without extensionthrough a standard file dialog box (“File Dialog” function). The filesare opened (“New File” function), if and only if the chosen names do notexist; if either of the names exist, or the name is not a valid one, awarning is presented to the user (“Prompt for Termination.vi”). A set ofheader data is written to the Main Data File immediately. Finally, theelapsed time clock is started (“Start Time.vi”). Future timer readingscompared to this initial reading by simple subtraction to find thenumber of elapsed milliseconds. This simple algorithm has one knownflaw. When the timer reaches (2Λ32)−1, it wraps to 0. This will causenon-sensical data to be produced in the event that this wrapping occurs.It was not considered worth the trouble to fix this problem, given theincredible rarity of its occurrence. Any time stamp inconsistencies canbe corrected after the fact with relative ease. Loading and Acquisition:This section encloses the bulk of both the code and execution time forthis program. This discussion covers the actions taken by the programduring a normal pass through the main loop. The main loop is enteredonce for each given Time-Pressure-pair. At the beginning of the loop,the interval is divided into a large number of steps, and the pressureand time deltas for each step are calculated. An internal “stepper” loopis then begun. At each step, the program takes deflection and pressuremeasurements, and the corrects them for known systematic errors. Thegraphs and elapsed time indicators on the front panel are updated. Nextthe program enters a delay.

Shutdown: This phase produces a state which is safe both for data andspecimen before terminating program operation. The pressure is set tozero, releasing the specimen from applied forces. All time series arestored to disk file, and the file is closed (“Close File” function).System operation terminates at this point.

Subroutines: The following subroutines are used in this program. GeneralArithmetic and Conversion functions are not mentioned.

LabVIEW built-in functions: See the LabVIEW documentation for thesesubroutines.

Stop

File Dialog

New File

Path to String

Get Date/Time String

Concatenate String

Write File

Tick Count (ms)

Initialize Array

Build Array

Bundle

Format and Append

Close File

Computer Boards Universal Library functions: See the Universal Libraryand LabVIEW Extensions documentation sets.

Ain.vi

Aout.vi

ErrMsg.vi

Custom Subroutines: The following functions were developed specificallyfor this program. They are all completely documented below.

Continue.vi

Set Regulator Once.vi

Read Pressure.vi

Read Pressure Once.vi

Read Deflection Once.vi

Read Voltage Once.vi

Custom Subroutines: Discussion of each VI contains a number of sections.The Arguments list contains the names and types of each of the possibleincoming controls. The Returns list contains the names and types of eachof the possible outgoing indicators. The Subroutines Used List listseach contained function or SubVI for cross reference purposes. GeneralArithmetic and Conversion functions are not mentioned. Finally, theFunction section describes in some technical detail exactly how the VIproduces outputs from its inputs.

Read Voltage Once.vi:

Arguments: Board Number (Unsigned 32 bit integer), Channel Number(Signed 32 bit integer), Range Setting (Signed 32 bit integer)

Returns: Voltage (double), Error Message (String)

Subroutines Used:

Ain.vi

ErrMsg.vi

Function: This VI uses the Universal Library Routines from ComputerBoards to interface with the data acquisition card. Consult theappropriate documentation for the internal operation of this VI.Continue.vi

Arguments: Action Prompt (String)

Returns: True Boolean

Subroutines Used: None

Function: Used to force a pause in the program for user prompting. Popsup a dialog-like box. Set Regulator Once.vi

Arguments: Board Number (Unsigned 32 bit integer), Channel Number(Signed 32 bit integer), Pressure to Set (Double), Pressure Units (RingControl)

Returns: Error Message (String)

Subroutines Used: Aout.vi, ErrMsg.vi

Function: This VI sets the pressure the regulator is to apply. Itdetermines the pressure range by the channel number (the properregulator must be connected to the proper output channel).

Read Pressure.vi

Arguments: Averaging Cycles (Signed 32 bit integer), Output Units (RingControl), Range Selector (Ring Control)

Returns: Pressure Measured (Double)

Subroutines Used: Read Pressure Once.vi

Function: Averages individual pressure readings for the number of cyclesspecified in the range specified. It then outputs the averaged value inthe specified pressure units.

Read Pressure Once.vi

Arguments: Board Number (Unsigned 32 bit integer), Gauge Number(Unsigned 32 bit integer), Output Units (Ring Control)

Returns: Pressure Measured (Double), Voltage Measured (Double), ErrorMessage (String) Subroutines Used: Ain.vi, ErrMsg.vi

Function: This VI reads the voltage value present in the specified boardand port, and returns both that voltage (in volts) and the associatedpressure (in the specified units).

Read Deflection.vi

Arguments: Averaging Cycles (Signed 32 bit integer)

Returns: Deflection Voltage (Double), Error Message (String)

Subroutines Used: Read Voltage Once.vi

Function: Reads and averages the voltage present on the deflectionsensor channel over the number of sampling cycles given in the argument.

Returns: Error Code (Signed 32 bit integer), Valve State (Boolean)

Once given the above disclosure, many other features, modifications, andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications, and improvements are, therefore, considered tobe a part of this invention, the scope of which is to be determined bythe following claims.

We claim:
 1. An apparatus for bulge testing films, the apparatuscomprising: a mounting structure including an upper surface and a cavitydefined therein; means for positioning a film to be bulge tested on saidupper surface over top of said cavity; a laser triangulation transducerfor measuring out of plane deflection or bulging of the film proximatesaid cavity; and means for determining stress and modulus properties ofthe film without any associated peeling of said film from said mountingstructure based upon measurements taken by said laser triangulationtransducer.
 2. The apparatus of claim 1, said laser triangulationtransducer including means for measuring deflection or bulging of thefilm by detecting deflection of a center area of the film relative tostable or non-deflected areas of the film spaced from the cavity.
 3. Anapparatus for bulge testing films, the apparatus comprising: a mountingstructure including an upper surface and a cavity defined therein; meansfor positioning a film to be bulge tested on said upper surface over topof said cavity; an optical transducer for measuring out of planedeflection or bulging of the film proximate said cavity in anon-contacting manner without any associated peeling of the said filmfrom said mounting structure, wherein said transducer is one of a whitelight interferometer and a laser triangulation transducer; and means fordetermining stress and modulus properties of the film based uponmeasurements taken by said transducer.
 4. The apparatus of claim 3,wherein said transducer is located directly above said cavity so as tomeasure film deflections.
 5. A structure for use in bulge testing offilms, the structure comprising: a membrane structure including aplurality of cavities defined therein; and a plurality of freestandingportions located on a single substrate capable of bulging, each of saidfreestanding portions corresponding to at least one of said cavities, sothat each of said freestanding portions defines part of a correspondingone of said cavities, and wherein each of said freestanding portions isadapted to receive thereon a film to be bulge tested at a plurality ofdifferent locations over said single substrate without causing the filmto peel from said membrane portions.
 6. The structure of claim 5,wherein the film to be bulge tested includes one of a thin metal film, athin ceramic film, a coating, and a layer; and wherein said film to bebulge tested is from about 100 Å to 500,000 Å thick.
 7. An apparatus forbulge testing films, the apparatus comprising: a mounting structure; amembrane structure rigidly and hermetically coupled and bonded to themounting structure; and a mounting wax having a solid to liquidtransition temperature greater than about 40° C. used to bond themembrane structure to the mounting structure for bulge testing andreduce the introduction of stresses into said membrane structure.
 8. Theapparatus of claim 7, wherein the mounting wax has a transitiontemperature greater than or equal to about 60° C.
 9. The apparatus ofclaim 8, wherein the mounting wax has a wax to liquid transitiontemperature of greater than about 80° C.
 10. An apparatus for bulgetesting films, the apparatus comprising: a mounting structure includingan upper surface and a cavity defined therein; a computer-controlled XYZmaneuverable stage system for manipulating the mounting structure threedimensionally; means for positioning a membrane structure on the uppersurface of the mounting structure; an optical transducer for measuringdeflection or bulging of a film proximate said cavity in anon-contacting manner without any associated peeling of the film fromsaid mounting structure; and means for manipulating said mountingstructure three dimensionally in order to center the optical transducerover top of a central portion of the film to be bulge tested.
 11. Theapparatus of claim 10, further including means for bulge testing thefilm, the film having a thickness from about 100 Å to 500,000 Å.
 12. Theapparatus of claim 11, wherein the film has a thickness of from about100 Å to 50,000 Å.
 13. An apparatus for bulge testing films, theapparatus comprising: a mounting structure including an upper surfaceand a plurality of cavities defined therein; a computer-controlled XYZmaneuverable stage system for manipulating the mounting structure threedimensionally; means for positioning a membrane structure having aplurality of freestanding membrane portions located on a singlesubstrate on the upper surface of the mounting structure; an opticaltransducer for measuring deflection or bulging of a film at a pluralityof different locations proximate each of said cavities in anon-contacting manner; and means for manipulating said mountingstructure three dimensionally in order to center the optical transducerover top of a central portion of a selected portion of the film to bebulge tested.